Skip to main content

pick

pick creates a synchronous transform that keeps selected own enumerable fields.

import {pick, pipe, rename} from 'shapewire';

const selectUser = pick(['user_id', 'full_name']);
selectUser({user_id: 7, full_name: 'Ada', email: 'ada@example.com'});
// {user_id: 7, full_name: 'Ada'}

Signature and inference​

pick(keys)(input);
pick<Input>()(keys)(input);

Inline arrays infer precise keys without as const; mutable and readonly arrays are accepted. The explicit-input form validates keys immediately:

type ApiUser = {user_id: number; full_name: string; email: string};
const toListItem = pick<ApiUser>()(['user_id', 'full_name']);
// Transform<ApiUser, {user_id: number; full_name: string}>

Pipelines and ordering​

const toUserListItem = pipe(
  pick(['user_id', 'full_name', 'avatar_url']),
  rename({user_id: 'id', full_name: 'name', avatar_url: 'avatarUrl'}),
);

Place pick after rename when selecting renamed keys. It can also be combined with omit; this is normal composition, not a configuration conflict:

pipe(pick(['id', 'name', 'email', 'token']), omit(['token']));

Behavior and edge cases​

  • Returns a new normal plain object and never mutates the input.
  • Is shallow: nested objects, arrays, functions, and other values are retained exactly.
  • Ignores missing runtime keys, duplicates, inherited fields, and non-enumerable fields.
  • Supports string, numeric, and symbol property keys. Requested order is used, subject to JavaScript's integer-key enumeration rules.
  • Reads a retained getter once and stores its value as a data property; descriptors are not preserved.
  • Safely copies __proto__, constructor, and prototype without changing the result prototype.
  • Frozen and sealed inputs are supported.
  • The typed API is for object records. At runtime, nullish values and string/number/boolean primitives throw TypeError; arrays and functions are treated as objects.

Use pick for intentionally small view models or allowlist-style public boundaries. Do not use it for deep selection, validation, asynchronous work, or descriptor-preserving clones.